Fuel injectors convert fuel into a fine spray which is mixed with air in engine combustion chambers. The major advantage of the system is that the amount of fuel being mixed with air can be more precisely controlled and the mixture can be more evenly spread throughout the air coming into the engine. In combination with an electronic computer which monitors engine conditions and exhaust emissions, fuel injection can increase fuel efficiency and reduce pollution.
Fuel injection was adapted for use in petrol-powered aircraft during World War II and was first used in a car in 1955 with the introduction of the Mercedes-Benz 300SL Fuel injection became widespread with the introduction of electronically controlled fuel injection systems in the 1980s and the gradual tightening of emissions and fuel economy laws.
Today, fuel injection is conventionally used in diesel engines. The diesel engine is a type of internal combustion engine; more specifically, a compression ignition engine, in which the fuel is ignited by the high temperature of a compressed gas, rather than a separate source of energy, such as a spark plug. Many modern diesel engines use direct injection, in which the injection nozzle is located inside the combustion chamber. Today automobile manufacturers conventionally use fuel injection with gasoline engines.
A commonly used injector utilizes a closed-needle injector having a needle valve assembly which utilizes a spring-biased needle positioned adjacent to the orifice of a fuel metering chamber. The needle reciprocally operates to open and close communication between a fuel metering chamber and the engine combustion chamber allowing fuel to be injected into the cylinder and resisting blow back of exhaust gas into the fuel metering chamber of the injector. In many fuel systems, when the pressure of the fuel within the fuel metering chamber exceeds the biasing force of the needle spring, the needle moves outwardly to allow fuel to pass through the orifice(s) of the fuel metering chamber, thus marking the beginning of injection.
In another type of system disclosed by U.S. Pat. No. 5,676,114 to Tarr et al., the beginning of injection is controlled by a servo-controlled needle. The assembly includes a control volume positioned adjacent an outer end of the needle valve, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve. U.S. Pat. No. 5,463,996 issued to Maley et al. discloses a similar servo-controlled needle valve injector.
U.S. Pat. No. 5,458,292 to Hapeman discloses a fuel injector with inner and outer injector needle valves biased to close respective orifices and operable to open at different fuel pressures. The inner needle valve is reciprocally mounted in a central bore formed in the outer needle valve. However, the opening of each needle valve is controlled solely by injection fuel pressure acting on the needle valve in the opening direction such that the valves necessarily open when the injection fuel pressure reaches a predetermined level.
United Kingdom Patent Application No. 2266559 to Hlousek discloses a closed needle injector assembly including a hollow needle valve for cooperating with one valve seat formed on an injector body to provide a main injection through all the injector orifices and an inner valve needle reciprocally mounted in the hollow needle for creating a pre-injection through a few of the injector orifices.
U.S. Pat. No. 5,199,398 to Nylund discloses a fuel injection valve arrangement for injecting two different types of fuels into an engine which includes inner and outer poppet type needle valves. During each injection event, the inner needle valve opens a first set of orifices to provide a pre-injection and the outer needle valve opens a second set of orifices to provide a subsequent main injection. The outer poppet valve is a cylindrical sleeve positioned around a stationary valve housing containing the inner poppet valve.
U.S. Pat. No. 5,899,389 to Pataki et al. discloses a fuel injector assembly including two biased valve elements controlling respective orifices for sequential operation during an injection event. A single control volume may be provided at the outer ends of the elements for receiving biasing fluid to create biasing forces on the elements for opposing the fuel pressure opening forces. However, the control volume functions in the same manner as biasing springs to place continuous biasing forces on the valve elements. As a result, the needle valve elements only lift when the supply fuel pressure in the needle cavity is increased in preparation of a fuel injection event to create pressure forces greater than the closing forces imparted by the control volume pressure.
Other types of injectors are coupled to a fuel supply which delivers fuel to a pump chamber within the fuel injector at a predetermined supply pressure, this pressure then being increased within the fuel injector to a higher injection pressure to effect actuation of the needle valve assembly. A commonly used means to increase pressure within the storage chamber includes plunger which reciprocates within the pump chamber which is actuated by an engine driven cam or other reciprocating means. Fuel in the pump chamber is delivered to the fuel metering chamber at a pressure sufficiently high to move the needle from the valve seat.
In one form of such a fuel injector, the plunger is provided with helices which cooperate with suitable ports in the pump chamber to control the pressurization and therefore the injection of fuel during a pump stroke of the plunger.
In another form of such a fuel injector, a solenoid valve is incorporated in the fuel injector so as to control, for example, the drainage of fuel from the pump chamber. In this latter type injector, fuel injection is controlled by energizing the solenoid valve. An exemplary embodiment of such an electromagnetic fuel injector is disclosed, for example, in U.S. Pat. No. 4,129,253 to Ernest Bader, Jr., John I. Deckard and Dan B. Kuiper.
Other types of fuel injection systems may use piezoelectric actuators or elements, in which the piezoelectric actuators or elements exhibit a proportional relationship between an applied voltage and a linear expansion. Thus, it is believed that using piezoelectric elements as actuators may be advantageous in fuel injection nozzles for internal combustion engines as disclosed by European Patent Specifications EP 0 371 469 B1 and EP 0 379 182 B1.
An example of a fuel injector which uses the expansion and contraction of piezoelectric elements with double-acting, double-seat valves to control corresponding injection needles in a fuel injection system is shown by German Patent Applications DE 197 42 073 A1 and DE 197 29 844 A1.
As can be understood from the above discussion, there is a large commercial market for fuel injectors for use in various types of reciprocating, rotary and other types of engines which has wide application in automotive and aircraft industries with respect to both compression ignition and spark ignition engines.
First, with respect to compression ignition engines, there is a compelling argument for stronger penetration in the market as a means of reducing CO2 emissions. With the focus of the Kyoto Protocol on emissions of greenhouse gases, and the contribution of transportation sources to this problem. Moreover, compression ignition engines are able to extract almost double the useful work than conventional spark ignition engines.
However, while compression ignition is an attractive solution for CO2 reduction, exhaust emissions associated with diesel fuel are increasingly coming under the environmental spotlight. Most notable are the oxides of nitrogen (NOx) and particulate matter (PM), which are regarded almost exclusively as “diesel problems”. The difficulty in meeting the increasingly stringent limitations on particulate and NOx emissions has stimulated interest in ethanol-fueled compression ignition engines because ethanol diffusion flames produce virtually no soot. Unfortunately ethanol does not have suitable ignition properties under typical diesel conditions because the temperatures and pressures characteristic of the diesel engines causes a longer ignition delay while using ethanol. Therefore, in order to make use of ethanol in a diesel engine, either a system to improve the ignition quality of ethanol or an ignition aid may be necessary.
Similarly, compression ignition engines can be operated with fuels made from other organic stock such as soybeans, rapeseed, and animal tallow produced through a process called transesterification which removes fatty particulates that cause coking and other problems in diesel engines. These additional bio-fuels used undiluted or mixed with diesel fuel have demonstrated reduced particulate emission. However, as the concentration of bio-fuel is increased cold engine start may require additional engine cranking and cold engine operation may be substantially inferior to diesel fuel. Similarly, in order to make use of bio-fuels either a system to improve the ignition quality of bio-fuels or an ignition aid may be necessary.
Second, with respect to lower compression spark ignition engines, the composition of fuels and the manner of operation, especially in automobiles, has significantly altered over the past thirty years. To meet air pollution regulations in the United States, and in other countries, the lead in gasoline was removed substantially lowering octane of the fuel. To compensate for the lowered octane, automobile manufacturers altered the timing in cars to prevent the resulting “ping” or “knock” and to reduce NOx formed at higher combustion temperatures and pressure.
In spark ignition engines, as you advance timing from top dead center, both peak combustion temperatures and peak cylinder pressures go down (as does “knock” and the production of NOx). At some point, however, spark ignition comes too early and the pressure produced from combustion works against the piston (on the up stroke) more than it works with the piston (on the down stroke).
In newer vehicles, how much fuel to deliver to the fuel combustion cylinder and when to provide ignition spark is typically monitored by computers which use sensors to detect engine “ping” or “knock” and to reduce emissions; however, the amount of ignition control that can be achieved under a broad range of operating conditions may be insufficient to completely eliminate “ping” or “knock” under certain circumstances, for example when low octane fuel is used. Also, the computer may be reacting to something that is already happening or has happened, and engine “ping” or “knock” has the potential to be harmful with relatively few occurrences.
Third, aviation remains the only transportation industry in the United States whose engine emissions are not yet regulated. The piston engine fleet uses the only fuel still containing lead as an octane enhancer. While turbine engine manufacturers have dedicated considerable resources to reduce engine emissions, the airline industry has experienced unprecedented growth and the aggregate pollution has increased dramatically. In addition to the problem caused locally by pollutants, fossil fuels used in aircraft worldwide have a significant impact on global warming because of the altitude at which they are emitted. Therefore, there are two pending crises in the aviation world: 1. the mounting pressure to remove lead from the aviation gasoline used by the piston engine fleet, and 2. the commercial aviation's environmental impact escalating both at the local and global level.
With the removal of lead from aviation fuel, use of the resulting lower octane fuel will require technical innovations to avoid “ping” and “knock”. Because existing technology may not allow sufficient ignition control to eliminate “ping” and “knock” under certain circumstances and aircraft engines may then experience increased wear similar to that experienced in automobile engines using lower octane fuels.
Also, the Federal Aviation Administration has provided certifications for engines and aircraft powered by ethanol. Supplemental Type Certificates have also been issued for the use of 100% denatured ethanol for the IO-540 series of 260 HP Lycoming engines, for the O-235 series of Lycoming engines, and the Cessna 152 series of training aircraft. In May of 2000, dual fuel certification was obtained for a Piper Pawnee, an agricultural spray aircraft for the use of either ethanol or Avgas.
While aviation applications of bio-fuels are economically competitive with aviation fossil fuels, and are actually less expensive if the real cost of the fossil fuels is taken into account, the use of bio-fuels may be limited due to reduced performance of aviation engines under certain conditions as above-described and may require an ignition aid.
The instant invention can address certain aspects of the problems encountered by the use of lower octane or bio-fuels in fuel injected spark ignition engines.